1. Field of the Invention
The present invention relates to molded thermoplastic articles that have a mineral appearance. This invention relates to thermoplastic articles molded with synthetic resin chips for imparting a granite or other varicolored appearance to the article.
2. Description of the Related Art
Mineral appearing molded synthetic resin articles are being fabricated into commercially attractive, prestigious cabinets, vanities and other decorative items. These mineral appearing molded synthetic resin articles are commercially available as flat sheets and as sinks and basins. Fabrication of these articles into decorative items is being achieved with commercially available woodworking tools and techniques. (See U.S. Pat. No. 5,043,377)
The synthetic resins used for molding these articles can be commercially available transparent, unsaturated polyester or cross-linked methyl methacrylate thermosetting resin forming compositions. The synthetic resins used for producing these articles are highly filled with mineral particles having substantially the same refractive index as the cured matrix synthetic resin. The mineral particles have particle sizes less than about 50 microns for producing articles in which the mineral particles are transparent.
Molded articles filled with 50 to 80 percent by weight of the molded article of mineral particles have surface hardnesses approaching the surface hardness of minerals. Surface hardnesses along with the transparency of the matrix synthetic resin of these molded articles contribute substantially to their commercial attractiveness. (See U.S. Pat. Nos. 3,396,067 and 3,405,088)
Alumina trihydrate (Al.sub.2 O.sub.3 .multidot.3H.sub.2 O) can be use as the mineral particles. Alumina trihydrate releases water when heated for imparting reduced flame spread and smoke density to the molded article. Articles molded with commercially available unsaturated polyester resin and filled with alumina trihydrate can meet flame spread and smoke density requirements for construction materials. (See U.S. Pat. Nos. 3,780,156; 3,827,933; 4,193,908 and 5,164,425)
A granite or other varicolored mineral appearance can be achieved with these molded articles by incorporating synthetic resin chips in the synthetic resin forming composition. The chips can be opaque or translucent for providing visibility for the chips in the molded article. Pigmented chips can provide a color contrast between the chips and the matrix synthetic resin of the molded article. The size and concentration of these chips are selected to provide a molded article with a commercially attractive appearance. Particle sizes of 50 to 3000 microns can be used. The chips can constitute from 2 to 15 parts by weight of the molded article. (See U.S. Pat. Nos. 4,085,246; 4,159,301; 4,433,070; 4,544,584; 4,961,995; 4,983,668 and 5,032,625)
It has now been discovered that certain chips for achieving the varicolored mineral appearance can increase the surface hardness of molded articles and reduce the ASTM Smoke Index for the article.